A study published in Nature shows us that both evolution and genetics have made a big impact on the behavior of humans…including in the case of murder. However, as we have become more civilized, these instincts have been muted.

Scientists have looked at the rate of homicide in more than 1,000 species, and they noticed something interesting: The rates of these lethal acts are similar, which means that evolution of each species can give us a good idea of how violent each species really is.

This study states that humans are part of a violent group of similar mammals. These mammals all evolved at the same time, together. Plus, all of these mammals have murderous and violent pasts. So, what does this mean for us? It means that we are violent today because our ancestors were violent.

When you look at all mammals, about three in 1,000 are murderers. However, when you specifically look at humans, the average over time is about 20 in 1,000. Furthermore, when you examine certain time periods, such as the medieval period, this rate rose to about 120 murderers in 1,000. These numbers have fortunately fallen, however, and today, it stands at about 13 murderers per 1,000 people.

So, we are killing each other much less frequently today than we used to 1,000 years ago. However, we are still not as peaceful as other mammals. For instance, killer whales, which we believe to be quite violent, have a murder rate of almost zero against their own species.

We are much more violent than whales, but when we compare our murder rates to those of cougars, baboons, or lemurs, we are less violent. All of these animals have a murder rate of about 100 per 1,000.

Since this research looked at violence by comparing species that are closely related, it is not surprising that these species are similarly violent. It is also interesting that the more closely related a species is, the more similar their instances of violence.

It’s quite difficult to actually calculate the rates of violence among our ancestors, but we are able to get a good idea thanks to archaeological evidence. It was found that by looking at these sites, that violence rates were lower among people who had some type of government or culture. This also suggests that murder rates among a species can be reversed. In fact, this evidence shows that it can decrease or increase based on ecological, cultural, or social factors. This evidence is similar to what was found in a study done at Harvard, which specifically looked at violent crimes including rape and murder.

When looking at these facts, we find that humans are territorial and social, but also naturally violent. As we have developed over time and found more civilized activities, our rates of violence have gotten lower. What’s even more interesting is that most mammals aren’t murderers towards their own species…but some, such as lions, wolves, and primates, which includes humans, engage in violent actions.